NetPlayServer: handle port forwarding in constructor

Source/Core/DolphinWX/NetPlay/NetPlayLauncher.h

@@ -34,9 +34,7 @@ public:
 
   std::string game_name;
   u16 listen_port = 0;
-#ifdef USE_UPNP
-  bool forward_port;
-#endif
+  bool forward_port = false;
 };
 
 class NetPlayJoinConfig : public NetPlayLaunchConfig